Integrated electronic circuits are usually fabricated with all internal connections set during the manufacturing process. However, because of the high circuit design and development costs, as well as high tooling costs for making such circuits, a new type of integrated circuits is appearing in the integrated circuit marketplace. These circuits are called user-programmable circuits because a user may program them using a series of programmable links within the circuit. Programmable links are electrical interconnects that the user breaks or makes at selected electronic nodes in the fully fabricated and packaged integrated circuit device. These interconnects occur by programming which activates or deactivates the selected electronic nodes to make the integrated circuit perform the desired functions or set of functions that the user desires.
One type of programmable link, the antifuse link, creates a short or relatively low resistance (e.g., less than 1 K.OMEGA.) link between two or more connectors. Antifuse links, or simply antifuses, consist typically of two conductor or semiconductor elements having some kind of dielectric or insulating material between them. During programming, the dielectric at selected points between the conductive elements breaks down due to a current that develops from applying a pre-determined programming voltage to the conductive elements of selected antifuses. This electrically connects the conducting or semiconducting elements.
Undesirable capacitances and leakage currents of unused antifuses are problems that occur in user-programmable integrated circuits that use antifuses. That is, the antifuse, which is normally an open device in its unprogrammed condition, has an associated leakage current between the connectors and produces some degree of capacitance between the connectors. Some antifuses have different characteristics in their non-programmed state. For example, some have lower capacitance (e.g., in the 1 pF range) and others have larger capacitances (e.g., in the 8 pF range). Some antifuses, on the other hand, have lower leakage current levels than others (e.g., less than 1 nA verses 30 nA). They all, however, have leakage currents and capacitances that adversely affect the operation of the user-programmable integrated electronic circuits that use them.